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Dec. 8, 1936. A. o. MERRILL TREATMENT OF DIGESTION LIQUORS 2 Sheets-Sheet 1 Original Filed July 15, 1932 ATTORNEY 8, 1936. A. D. MERRILL TREATMENT or DIGESTION LIQUORS OrigihaIFiled July 15, 1932' 2 Sheets-Sheet 2 ATTORNEY Reiseued Dec. 8, 1936 UNITED STATES 35 Claim.

This invention relates to the digestion of fibrous material, and more particularly to the treatment of digester liquor. The object of the invention is the provision of improvements in methods and 5 apparatus for the digestion of fibrous material and in particular for the treatment of digester liquors.

My invention results in the production of an improved and uniform pulp, as a result of im- 10 provements in the liquor circulating apparatus.

In my preferred operation, the circulation of the liquor is considerably slower than has heretofore been the practice in the sulphite process. My apparatus for circulating and heating sulphite l5 'digester liquor includes steam coils within the vertical digester, circulation of the liquor being effected by means of a pump located outside the digester. The cook is not subject to interruption in the case of trouble in the circulating apparatus, and little or no deposit on the heating coils results even though the circulation should be interrupted during the cook.

I provide for the rapid withdrawal of side relief liquor at the initiation of the cook, thus preventing the entrance of contaminated liquor into the accumulator or acid storage tank. At the end of the cook I prefer to stop the circulation and to admit steam directly into the digester, and I haveprovided an improved method and apparatus for degassing the digester liquors at the end of the cook. Circulation of the liquor is accomplished through the blow ofl elbow of the digester, and this construction results in decided advantages due to elimination of the cost and 3'5 difliculty of maintaining entrances through the lower part of the digesterwall.

For a better understanding of my invention, a preferred embodiment thereof is illustrated in the accompanying drawings, in which:

40 Fig. l is a diagrammatic elevation of a preferred digester system, certain parts being omitted for the sake of clearness;

Fig. 2 is a horizontal section through the digester on the line A-A of Fig. 1 showing one 45 form of strainer on the suction end of the circulation line;

of strainer;

Figs. 4 and 5 are elevation and vertical see so tional views respectively, illustrating the prefered construction of the strainer pipe; and

Fig. 6 is a die elevation of the blow oil elbow and connecting apparatus, illustrating an alternative connection to the circulating lines.

In thedrawings, the numeral l indicates sul- I Re. 20,200

PATENT OFFICE" TREATMENT OF DIGESTION LIQUOBS Albert D. Merrill, Watertown, N. Y., assignor to Chemipnip Process Ina, Water-town, corporaflon New York Original No. 1,945,594, dated January 30, 1934,

Serial No. 622,619, July 15, 1932. fol-reissue January 29, 1935, Serial No. 3,986

N. Y., a

Application phite digesters provided with gauge glasses. 8. While three digesters are shown, any number, connected as indicated, may be used. 00 is either an acid accumulator or cold acid storage tank. The relief line 44 provided with the valve 43, and the relief line 42 provided with valves ll and I1, communicate through the valve 46 with the line 45 and thence with the usual relief header 48. The header 8 leads to the eductor I0 I, which also connects through the valve 55 with the raw liquor supply line 56. Theeductor IIH connects with the drop leg 58 which leads through the similar eductor III! and the fitting 9| into the bottom of the acid accumulator. The operation of these relief connections may be in accordance with the disclosure of the co-pending application of T. L. Dunbar and A. D. Merrill, 'Ser. No. 576,254, filed Nov. 20, 1931, (now Patent No. 1,918,459, issued July 18, 1933) and forms no part of the present invention. I

cumulator through the T 93, valves 94 and IJII and pump I94, to the connections ll, i4 and 9,

through valves ii and Ill. The accumulator liqnor may thus pass to the branchw I having therein valves "and check valves 2| and entering the blow of! elbow ill.

The steam header 28 communicates through the line 25, valves Ill and 23 and check valve 24 with the bottom of the blow oil elbow. The header 2! also connects through the line ti and fitting 28, valves 29 and I03 and check valve 30, with the heating coil 5 inside the digester.

The valve 29 is provided with the thermostatic control I which is of a known type and operates automatically to shut ofl? the steam when the temperature in the digester has reached a predetermined point. If desired the valve 29 can also be connected with a cam and timing mechanism so that the temperature in the digester is controlled thereby.

Condensate from the coils 5 passes through the lines 32 and. 94 and valve 33 to the condensate selector 3, from which uncontaminated condensate passes through the line 36, valve 31, line 38 and header 39 to the hot well. If the condensate should become contaminated with acid liquor, the selector, I automatically passes the contaminated condensate through the line to the sewer.

Y The circulating line Ii, preferably surrounded by insulation to prevent loss of heat by radiation, leads from the upper part of the digester to the suction side of the pump 2. The suction end of the circulating line H enters the upper part-of the digester through the valve 00, and is provided inside the digester with the strainer 6. In Figs.

2 and 3 I-have shown two forms of the suction end strainer 0, either ofwhich gives excellent results. The strainer may extend diametrically across the digester, as shown in Fig. 3, or it may be circular in form, as shown in Fig. 2, resting on the supports 49. The strainer is positioned in the digester so as to slope slightly toward the valve 50. A preferred construction of the suction end strainer pipe is shown in more detail in Figs. 4 and 5, liquid inlet holes 02 being bored only in the upper half of the strainer pipe. It has in the past been customary to bore inlet holes around the entire circumference of circulation strainers, and the result of this construction is that practicaily-all of the liquor is taken out of the digester in the neighborhood of the digester wall or where the suction is applied. In my construction of the suction end strainer the liquor is drawn in through the perforated upper half of the strainer B and runs along the imperforate lower half thereof to the circulating line. The pressure existing in the digester and the suction effect of the circulating pump assist in dr'awing the liquor through the perforations. I

The pump 2 discharges through the line I2 and valve ii to the connection I4 and thence through the valve I0 and line 0 into the lines I, which lines, as stated above, enter the blow of! elbow. While I have shown a plurality of entrances through the blowoif elbow, excellent results may be obtained with only one entrance into the bottom of the elbow, as shown in Fig. 6.

The line I2 also connects through the valve I0 with the relief header 22. The header 22 leads to the accumulator 00, either through the valve 00 and the T 02 or through the line 20, valve 00 and fitting 0i. The line I20, provided with the valve 'I2I, leads from the blow ofi elbow to the suction side of the pump 2. .The line I22, provided with the valve I20, leads from the discharge line I2 of the pump.

2 into the digester near the top thereof. On the end of the line I22, and within the digester, I provide the spray connection I24. The line I20 is provided with a strainer (not shown) at' its termination inside the blow of! elbow I I0. At thev end of the cook it is thus possible, by proper manipulation of the valves as hereinafter described, to utilize the pump 2 to withdraw digester liquor from the bottom of the digester and spray the same into the top thereof, resulting in liberation of gas which passes out through the top relief connection.

The pump 00 connects through the valve 0'! and line III with the filling header I0 at'a point behind the valve I30 on the suction side of ,the pump I04. .This pump 00 exhausts through the check valve 00 and valve I00 into the eductor I02 and thence through the fitting 0| into the accumulator. By these connections acid liquor from the accumulator may be circulated through with acid from the accumulator or acid storage tank '00 by means of the pump I04 and header I0. During the filling operation the valves 4i and 42,are closed. The valve I2 is also closed and valves I0, I4, 20, 04 and I20 are open. Liquor is thus pumped from the accumulator into the blow off elbow, through which it enters the digester. The valves 2| are check valves which close in the event that the pump I 04 should shut down due to lack of power or other cause.

The pump I04 is kept running until a hydrostatic pressure of approximately 50 lbs. is pumped on the digester. The valve I0 is then closed, and the valve I l in the discharge line I2 from the pump 2 and the valve 00 in the circulating line II are opened. The pump 2 is started and the digester liquor is circulated through the strainer B, valve 00; line II, pump 2, line I2, connection I4 and valves I2 and ii to the lines I and I and thence through the valves 20 and check valves 2| into the blow oil elbow- IIO, whence it passes up through the neck into the digester again.

As soonas the digester has been filled with acid the -valve I02 is opened, admitting steam from the steam header 20 tothe coil 0. From the coil 5 steam condensate is led to the selector. 3. From the selector, uncontaminated condensate passes to the'hot well while any contaminated condensate is automatically passed to the sewer. The condensate from the hot well may, of course, be utilized in a variety of ways. 1

It has heretofore been the practice to vent liquor through the side relief 42 at the beginning of the cook, by opening the valve 4i at temperatures between and 125 C. When operating in this manner, however,- it is sometimes impossible to draw on all of the side relief liquor with the necessary rapidity. Consequently some liquor which has been contaminated by constituents dissolved out of the wood may be carried over to the accumulator, thereby deteriorating the acid cooking liquor thereim.

I am able toavoid this contamination by drawing of! the side relif liquor through the circulating line I I. This I accomplish by closing the valve I3 and opening the valve I0, thereby causing the pump 2 to discharge into the header 22 and thence into the accumulator, either directly through the valve II and the T 02 or through the line 00, valve 50 and fitting II. This method of operation permits withdrawal of all the side relief liquor within a very few minutes. For example, the side relief from the digester is normally started at about 110' to 0., and in operation according to methods heretofore available the temperature in the digester often reaches 130 or higher before all of the side relief liquor can be withdrawn, resulting in the contamination of the accumulator liquor. with my improved method and apparatus,-however, I am able to withdraw all the side relief liquor in sucha rttimethatthe temperature in the digester does not rise high enough to result in contamination of the relief liquor (e. g., below 0.).

The side relief is continued until the liquor in the digester is brought to a predetermined level, which is ascertained by the gauge glass 0. After the liquor has been brought to this level the level remains practically constant until toward the endofthecookwhensteamisadmittedtothe' nor contains considerable 50: gas.

70.: digester liq- 1-;-

Theadmisslon ofsteamintotheooilliscon tinued until near the end of the cook. After theside relief liquor has been conducted to the accumulator the valve II is closed andthevalve lscpenedandcirculationoithedigeateriiqmr ismaintained.- Duringthecookthevalveilis opentoventreliefgasestotheheader.

It has been customary to continue circulation oithedigesterliquorthroughouttheentireperiod oi'the cook, but I have found that this is not only unnecessary but actually disadvantageous.

readily conducted. v

The digester liquor contains substantial amountsoifloaattheendoithe-ccitandsubstantial los resulis from running this spent digester liquor to the sewer. I have provided improved means for the digester liquor inside thedigester. Att'heendoithecookthe valves liandllareclosedandthevalves III and 12! are opened. The digester liquor is thus withdrawn irom'the bottom of the digester throughtheblowoii'elbowbythepumpiand in near the top oi the digester, whereby BOsisSllbstantiallyliberted therefrom, passesoii through therellet connection ll, and is recovered. The admission of steamthrough the line ilmaybecontinuedduringthisspraying operation.

I meter to circulate the cook at a much slower rate heretoiorebeenuniversally advocated. A complete circulation oi the digester liquor in i to minutes has been where direct heaters are used outside of the digesters, in order to obtain ascom'ingactionoitheliquorwithintheheater and prevent deposition of calcium or'magnesium salts. I have found that this rapid circulation is a disdvantage. With my method and apparatus 'itisimnecessary,andlamabletoproducea superior 1111 9 by a complete circulation oi the dlgester-liquor in from to 40 minutes, this time varying in accordance with the fibrous material being treated and local mill "conditions. This slower circulation means less horsepower required of the motor which drives the pump, and smaller circulating lines and pump, which reduces the costoitheinstallation. Further,theslowercirculation causes less liberation at 80: gas during the cook. Best results are obtained when the BOagasiskeptlntheliquor, asiaraspossible, throughout most of the cook. My method and apparatus greatly facilitate proper control oi the form pulp.

when using an indirect heater outside the dipump stops for any reason the exchange heater immediately clogs due to precipitation of calcium and magnesiinn salts. By placing steam coils withinthedigestes-Iamabletoccntinue the cook porarily stopped. The coils [are readily accessible ior cleaning it this should be necessary, but I'have round that by proper manipulation of the circulation there is no deposit on these coils. Another type of indirect heater, placed inside the digester, could be used.

the digester liquor during cooking operation and result in a much more uni-' gester for the digester liquor, ii the circulating.

without interruption even if the p mp is tom 'lheprei'erred construction of the straineronthe suction end oi the circulation line results in uniform withdrawal oi digester liquor from the upper part of the digester. through the blow oi! elbow I avoid the expensive maintenance oi inlets through the bottom part of the digester wall.

The rapid withdrawal of side relief liquorat the beginningot the cook preventscontaminationoi the liquor in the accumulator or acid storage tank.

withinthedigesterat the end of the cook.

results in material saving of S02.

'Ihe acid entering the digester may, with my method and apparatus, vary in temperature from to 110 0., whereas in the past the maximum temperature has been 50' C. I have obtained ex By circulating liquor cellent results employing hot acid containing 6 to 8% total 80:, combined 80: from 3% to 1.4%, the balance free 80:. The temperature of the liquor should not reach 110 C. until after .thorough penetrationoi the liquor into the chips, but by using combined hot acid and circulation I cut down the penetration period very materially; By starting the digester with acid at a temperature of 80 to 110 C., in connection with circulation, the cooking time for any given quantity of pulp is reduced. v

The maximum temperature is also reduced sev eral degrees by this combined hot acid indirect heating and circulating method, and I am able to produce-a very high quality pulp with a maximum temperature of 125 C. in a total cooking time of less than ten hours.

I claim:

' l. In apparatus of the character described, a digester having therein an indirect heat exchangenconduitsiw supp y steam to said heat exchanger and directly to the interioroi the digester, a conduit positioned without the digester and connecting therewith, means interposed in said conduit for circulating digester liquor through said conduit and through the digester, anda passage connecting said conduit and said circulating means with a storage receptacle .whereby liquor may be withdrawn from said conduit and passed thedigester.

'3. In apparatus of the character described, a

digester, a conduit connecting the upper part oi the digester with the lower part thereof, means :iorpassing liquor through said conduit, and a passageway for liquor so connecting said conduit with a storage receptacle that the means for passing liquor through the conduit may act to withdraw liquor irom the digester through said; conduit and to pass the same through said passageway to the storage receptacle, Y

4.- Apparatus as described in claim 3 including means for passing liquor from the storage receptacle into the conduit connecting the upper part of the digester with the lower part thereof, whereby liquor may be withdrawn from said storage receptacle and passed through said conduit intothe lower part of the digester.

5. In apparatus of the character described, a

' digester, a conduit connecting the upper part of said digester and entering the upper part thereof, above the point of entry of said first conduit, said second conduit terminating within the digesterat its upper end in means for subdividing liquor passing therethrough, and means for withdrawing liquor from the lower part of the digester and passing the same through said second conduit and subdividing means into the upper part thereof.

7. In apparatus of the character described, a digester, a conduit connecting the lower part of the digester with the upper part thereof, a pipe connecting the lower part of said digester with the upper part thereof and terminating at its upper end and inside the digester in means located above the normal liquor level for spraying liquor from the said pipe into the upper part of the digester, and a pump connected to circulate liquor through said conduit and also to force liquor through said pipe.

8. In apparatus of the character described, a digester, a conduit connecting with the upper part of the digester and entering the blow oi! elbow thereof through a plurality of entrances into said elbow, and means for circulating liquor through said digester, said conduit and said blow of! elbow.

9. In apparatus of the character described, a digester having therein an indirect heat exchanger, conduits for steam connecting with the interior of the digester and with the said heat exchanger, thermostatic means for controlling the entrance of steam into the heat exchanger, and means for circulating liquor through the digester.-

10. In apparatus of the character described, a'

digester, a pump, and a conduit connecting the digester with the suction side of the pump, said conduit connecting inside the digester with a suction end comprising an upper strainer portion and a lower imperforate channel portion, and a conduit connecting the discharge side of the pump with the inside of the digester.

11. In apparatus of the character described, a digester, a conduit connecting with the interior of said digester and terminating within the digester in a strainer having aperforated upper portion and an imperforate lower channel and so positioned within the digester as to slope toward the inlet end of said conduit, and meansfor withdrawing liquor from the digester through said strainer, passing the same through said conduit and returning the same to the digester.

12. In the digestion of fibrous material, charging a digester with fibrous material and filling said digester with acid liquor, withdrawing liquor from the digester at temperatures below 120 C. and passing the liquor thus withdrawn to a storage receptacle, then raising the temperature of the digester liquor above 120 C. by heating the same inside the digester without direct contact with the heating medium. andwithdrawing liquor from the upperfp art of the'digester and returningssaid liquortothe lower part thereof.

13. In'the digestion of fibrous material, digesting fibrous material with acidliquor under heat and pressure while indirectly heating said liquor withinthe digester and circulating said liquor by withdrawing the same from the digester and then returning it thereto at a rate which eiIects a complete circulation of the digester liquor in from 25 to 40 minutes.

14. In the digestion of fibrous material, digesting fibrous material with acid liquor under heat and pressure while circulating said liquor through the digester and heating the same without direct contact with the heating medium, then stopping said heating and circulation, and admitting steam directly to the contents the digester to complete the digestion-oi the fibrous material. v p

15. In the digestion of fibrous material, digesting fibrous material in heatedsulphite liquor, then liberating sulphurous gas fromsaid liquor by withdrawing liquor from the lower part oi the digester and returning the same in subdivided condition to the upper part thereof.

16. In the digestion of fibrous material, digesting fibrous material in heated liquor, then degassing the digester liquor within the digester by admitting steam into the digester and withdraw ing liquor from the lower part of the digester and spraying said liquor back into the upper part thereof.

17. Apparatus as described in claim bincluding means for passing liquor from said conduit into said receptacle.

18. In the digestion of fibrous material, charging a digester with fibrous material and with acid liquor, withdrawing liquor from the digester and passing it to a storage receptacle through a conduit connecting the upper part of the digester with said receptacle, then raising the temperature of the digester liquor, withdrawing liquor from the upper part of the digester through the said conduit and returning said liquor directly to the lower part of the digester.

19. In the digestion of fibrous material, digesting fibrous material in heated sulphite liquor, then liberating sulphurous gas from said liquor by withdrawing liquor from the lower part of the digester and spraying the same into the upper part of the digester.

20. In the digestion of fibrous material, digesting fibrous material in heated sulphite liquor while withdrawing liquor from the upper part of the digester and returning the same to the lower part of the digester, then liberating sulphurous gas from said liquor by withdrawing liquor from the lower part of the digesterand returning the same in subdivided condition to the upper part of the digester.

21. In the digestion of fibrous material, digesting fibrous material in acid liquor under heat and pressure while withdrawing liquor from the upper part of the digester and returning the same in a plurality of streams into the blow oi! elbow of the digester.

22. In the digestion of fibrous material, digesting fibrous material with acid liquor under heat and pressure and heating the liquor'within-the digester without direct contact with the heating means, then admitting steam directly to the contents of the digester to finish the digestion of the fibrous material.

: lati ng such liquor directly'to and from the accumulator and utilizing such recycle stream to absorb gases discharged Iran the digester.

' perature 24. In the digestion of fibrous material, digesting the material with acid liquor, while circulating the liquor to and from the digester, adding heat to the liquor during digestion without effectfining a volume of hot acid liquor in a pressure accumulatorycirculating such liquor to and from the accumulator while adding thereto hot reaction products from the digester.

25. In the digestion of fibrous material, digesting the material with acid liquor, while circulating the liquor to and from the digester, indirectly heating the liquor during such circulation; confining a volume of hot acid liquor in a pressure accumulator, circulating such liquor to and from the accumulator while adding thereto hot reaction products from the digester.

26. In the digestion of fibrous material, charging a digester with fibrous material, pumping preheated acid liquor to the digester while venting air therefrom, sealing the digester and pumping additional acid liquor into the digester until a high hydrostatic pressure is established therein; then circulating the liquor directly to and from the digester until the material is penetrated with the acid and then raising the mass to reaction temperatures.

2'1. In the digestion of fibrous material, charging a digester with fibrous material, pumping preheated acid liquor to the digester while venting air therefrom, sealing the digester against access of air and pumping additional hot acid liquor therein until a high hydrostatic pressure is obtained; then circulating the liquor directly to and ,from the digester until the material is penetrated with hot acid, raising the mass to reaction temand discharging hot fluids from the digester during the reaction; establishing a volume of hot liquor in a pressure accumulator, recirculating such liquor directly to and from the accumulator while utilizing such recycle stream to absorb the hot fluids discharged from the digester.

28. In the digestion of fibrous material, charging a digester with fibrous material and filling the digester with hot acid liquor under high hydrostatic pressure, circulating the hot liquor directly to and from the digester, maintaining the circulation under said high pressure until the material is penetrated by the acid, rapidly withdrawing liquor from the digester at temperatures below 120 C. and lowering the liquid level of such liquor, and then heating the liquor to raise the temperature of the liquor above 120 C.;' passing such withdrawn liquor to a high pressure accumulator and utilizing hot acid from the accumulator for charging another digester.

29. In the digestion of fibrous material, charging a digester with fibrous material, admitting hot therefrom, sealing the digester and forcing in additional hot acid liquor to establish a high try-I drostatic pressure on the acid liquor; circulating the hot liquor to and from the digester while maintaining the temperature below 110' C. to effect penetration of the material; then raising the mass'to reaction temperature, withdrawing hot relief fluids during reaction and passing such fluids into a volume of digestion liquor maintained in a pressure accumulator, and utilizing the preheated liquor in such accumulator to contact and digest material in another digester.

30. In the digestion of fibrous materials, charsing the material to a digester, forcing hot preing any substantial dilution of the liquor; con- 7 acid liquor to the digester while displacing air conditioned acid liquor into the digester while displacing air therefrom, sealing the digester and continuing the forcing of liquor intothe digester until a high hydrostatic pressure is established in the digester and recirculating the hot high pressure acid directly to and from the digester while maintaining the temperature of the liquor below 110 C. until the material is thoroughly penetrated with acid, then raising the liquor to 2 reaction temperatures.

31. In a process of the character described, charging a digester with fibrous material, introducing treating liquor into the digester until the latter is completely filled with the fibrous material and liquor, then sealing the digester and pumping additional liquor into the digester until a predetermined superatmospheric pressure is pumped on the digester, afterwards unsealing the digester, and then circulating such liquor through the digester.

32. In a. process of the character described, charging a digester with fibrous material, introducing treating liquor into the digester until the latter is completely filled with the fibrous material and liquor, then sealing the digester and pumping additional liquor into the digester until a prede termined superatmospheric pressure is pumped on the digester, afterwards unsealing the digester, and then circulating such liquor through the (igester until the temperature throughout the fibrous material in the digester is substantially equalized and raised to a substantially predetermined degree.

33. In a process of the character described, charging a digester with fibrous material, heating acid liquor in a separate receptacle by direct contact with digester relief fluids, forcing liquor from the receptacle into the digester until thelatter is substantially completely filled with the fibrous material and liquor; forcing additional hot liquor into the digester until a. predetermined elevated hydrostatic pressure is established on the liquor; circulating the liquor while maintained substantially at such presure directly to and from the digester and adding heat to the liquor during such recirculation.

34. In a process of the character described, charging a digester with fibrous material, heating acid liquor in a separate receptacle by a direct contact with digester relief fluids, forcing liquor from the receptacle into the digester until the latter is substantially completely filled with the fibrous material 1 and liquor, forcing additional hot liquor into the digester until a. predetermined elevated hydrostatic pressure is established on the 'liquor, circulating the liquor, while maintained substantially at such pressure, directly to and from the digester, adding heat to the liquor during such recirculation but maintaining the temperature below substantially 110 C. until thematerial is penetrated with the liquor and thereafter raising the mass to higher reaction temperatures.

35. In a process of the character described,

charging a digester with fibrous material, admitting hot acid liquor to the digester and in suflicient quantity to build up a hydrostatic pressure of the order of fifty pounds; recirculating the'liquor directly to and from the digester and adding heat to the liquor during such recirculation, controlling the amount of heat added to maintain the temperature below 110 C. until the material is thoroughly penetrated with acid, and then raising the mass to higher reaction temperatures.

ALBERT D. MERRILL. 

